About the Pet Age Calculator
Pets age faster than people, but not by a constant seven years for each year of life. Dogs and cats grow up quickly in the first two years and then age more slowly. This calculator shows the human-age equivalent of your pet using the common vet guide, which depends on the size of a dog, and compares it with the old times-seven rule and with a newer formula for dogs. Type your pet, its age in years and, for a dog, its size and the pet age in human years appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Pet Age Calculator
- 1Enter your pet, its age in years and, for a dog, its size.
- 2Pick the units or options from the menus if the pet age in human years tool offers them.
- 3Read the pet age in human years in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the pet age in human years
Owners use the figure to understand what their pet needs: puppies and kittens need a lot of care, mature animals need routine checks, and seniors need diet and joint support. Knowing that a 10-year-old large dog is like a person in their seventies explains why vet visits become more frequent.
Large dogs age faster than small dogs. A small dog is often called senior at 10 to 12, a giant breed at 6 to 7. Cats are less affected by breed, and indoor cats often live into their late teens.
How the pet age in human years is worked out
The vet guide counts the first year as about 15 human years, the second as 9 more, and then 4 to 6 more for each year, depending on size. The newer dog formula is human age = 16 × ln(dog age) + 31. A 5-year-old medium dog is about 39 in the vet guide, 35 by the times-seven rule and 56.8 by the newer formula. A 10-year-old large dog comes to 72, and a 10-year-old cat to 56.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Dogs by size and cats
- Three methods side by side
- Months accepted as decimals
Mistakes to avoid with pet age in human years
The three results differ because ageing is not the same for every animal, and the formulas are approximations. The newer formula was based on one breed of dog, the Labrador retriever. Use the figures as a guide and ask your vet for advice on your pet.
On phone and computer
On a phone, type into the boxes one after another and read the pet age in human years underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the pet age in human years move. The pet age calculator works the same on both. Your pet's age is only one part of its care. Use Age Calculator for exact dates, Calorie Calculator for feeding ideas, BMI Calculator for your own health, and Weight on Other Planets Calculator for a bit of fun.
Features
- Size matters for dogs
- Use as a guide
- Ask a vet
- Clear messages when the pet age in human years inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate pet age in human years?
The vet guide counts the first year as about 15 human years, the second as 9 more, and then 4 to 6 more for each year, depending on size. The newer dog formula is human age = 16 × ln(dog age) + 31. A 5-year-old medium dog is about 39 in the vet guide, 35 by the times-seven rule and 56.8 by the newer formula. A 10-year-old large dog comes to 72, and a 10-year-old cat to 56.
What is the formula for pet age in human years?
The vet guide counts the first year as about 15 human years, the second as 9 more, and then 4 to 6 more for each year, depending on size. The newer dog formula is human age = 16 × ln(dog age) + 31. The pet age calculator applies it exactly and rounds only the displayed answer to six significant figures.
Is one dog year really seven human years?
No. It is a rough rule. Dogs reach adulthood in about a year, which is like a teenager, and then age more slowly.
Where does the dog formula come from?
A 2020 study of Labrador retrievers compared the chemical changes in dog and human DNA and found age rising as 16 times the natural log of the dog's age plus 31.
How old is a 1-year-old cat?
About 15 in human terms, and 24 at two years, then four more for each year.
Is this pet age calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.